1. Field of the Invention
The present invention relates to a motor cooling structure for an electric vehicle using a driving motor as a power source or an auxiliary power source for running.
2. Description of Background Art
An electric vehicle using an electric motor as a power source has various advantages such that no air pollution occurs, noise pollution is suppressed, and acceleration/deceleration response is better as compared with a conventional automobile using an engine as a power source. However, at present, the electric vehicle also has various disadvantages, including a cruising distance that is short because of the limit of a battery capacity, and the cost per mileage of the unit energy is high causing low economy. A hybrid type electric vehicle is a vehicle capable of compensating for the disadvantages of such an electric vehicle driven by only an electric motor. Since a hybrid type electric vehicle has both an electric motor and an internal combustion engine, it also has the advantages of the electric vehicle and has now been put into practical use.
In vehicles having a belt type continuously variable transmission accommodated in a power unit case, the temperature inside the power unit case rises because of a frictional heat between a drive pulley and a belt and between a driven pulley and the belt. Japanese Patent Laid-open No. Sho 62-16530, for example, discloses a cooling structure for efficiently introducing an outside cooling air into a power unit case to lower the temperature inside the power unit case.
In an electric vehicle, a driving motor having a large calorific value is accommodated with a belt type continuously variable transmission in the power unit case. However, the above-mentioned conventional cooling structure is adapted to a power unit for a vehicle having an engine with a relatively small calorific value, because a heat source is limited to a transmission and a starter motor. Accordingly, if this conventional cooling structure is applied, without any changes, to an electric vehicle having a large calorific value, it is difficult to sufficiently cool the inside of the power unit case.